Narrow shoe journal microfinishing apparatus and method

ABSTRACT

A microfinishing machine and method especially adapted for processing of internal combustion engine crankshafts and other workpieces. Microfinishing is achieved by tooling having abrasive inserts or which present abrasive coated film against the journal to be machined. The tooling has a width less than one-half the length of the journal being machined. The narrow width tooling allows a range of workpiece configurations to be processed with common tooling, and through control of one or more of machining parameters including clamping pressure acting on the tooling, oscillation of the tooling, and stroking schedule of the tooling, desired journal contour profiles can be produced.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/289,382, filed on Feb. 1, 2016.

FIELD OF THE INVENTION

This invention relates to metal finishing and to an improved apparatusand methods for microfinishing metal cylindrical surfaces withparticular applicability for journal bearing surfaces of internalcombustion crankshafts.

BACKGROUND

Numerous types of machinery components must have finely controlledsurface finishes in order to perform satisfactorily. For example, finesurface finish control provided by an abrading tool or abrasive media,also referred to as microfinishing, is particularly significant inrelation to the manufacturing of journal bearing and cam surfaces suchas are found in internal combustion engine crankshafts, camshafts, powertransmission shafts, and other machine-finished surfaces. For journaltype bearings, very accurately formed journal surfaces are needed toprovide the desired hydrodynamic bearing effect which results whenlubricant is forced into the small clearance between the journal and theassociated bearing shell. Improperly finished bearing surfaces may leadto premature bearing failure and can limit the load carrying capacityand performance of the bearing.

Currently there is a demand for higher control of crankshaft journalbearing surfaces by internal combustion engine manufacturers as theresult of greater durability requirements necessary to offer improvedproduct warranties, the higher operating speeds at which engines(particularly in motor vehicles) are now required to sustain, and thegreater bearing loads imposed through increased efficiency and poweroutput capability of engines. Furthermore, there is an increasing demandfor improved performance for motor vehicle internal combustion enginesin terms of their fuel efficiency capabilities. Moreover, owners andoperators of such equipment require long service lives with low warrantyclaims and maintenance requirements.

In addition to journal bearings, numerous other types of machinedcomponents also require finely controlled surface finishes forrelatively rotating components, particularly in areas of sliding contactbetween parts.

Microfinishing for internal combustion engine crankshaft bearingjournals is accomplished presently using various types of machining andtooling systems. Microfinishing operations ordinarily take place after agrinding process which produces the desired journal geometry, but suchprocesses in general do not provide desired surface finish parameters.In typical microfinishing processes for crankshafts, the crankshaft isrotated about its main bearing journal axis and microfinishing toolingis brought to bear against the bearing surfaces, and upon rotation ofthe crankshaft, the machining action occurs. One approach uses abrasivestone tool inserts which provide the machining action. In anotherprocess type, abrasive coated film or tape is used as the machiningagent which is pressed against the bearing surfaces using rigid orcompliant tool insets such as formed from urethane type compositions orabrasive materials. The applicants have developed significantimprovements in the field of journal microfinishing including machiningapparatus and methods as described by U.S. Pat. Nos. 4,682,444;5,095,663; 5,148,636; and 5,531,631, the disclosures of which areincorporated by reference in their entirety.

Microfinishing approaches for crankshafts have generally sought toimprove the surface finish of a journal bearing surface without changingthe contour or geometry provided in the journal by prior machiningprocesses such as, most commonly, grinding operations. For simplehydrodynamic journal bearings, some engine manufacturers specify aslight barrel shape in the journal surface when viewed axially along thejournal surface to promote a desired hydrodynamic bearing effect.Although a so-called hourglass type profile in which the journaldiameter is minimum at near the center of the axial length of thejournal is less frequently desirable, it is specified for certainapplications. In other applications an idealized constant diametercylindrical surface is desired. In yet a further example of specificrequirements of engine manufacturers, some engine configurations have asplit pin crankshafts in which a single crankshaft journal supports twoconnecting rods and the journal is therefore comparatively long inlength. In those split pin applications, a “double barrel” type journalsurface profile may be desired. A crankshaft after grinding and beforemicrofinishing may not have the specified profile configuration.Crankshaft microfinishing operations available today are limited intheir capabilities of correcting geometric errors in incoming workpiecesand in forcing the workpiece to a desired profile configuration. It isan object of the present invention to provide capabilities duringmicrofinishing operations for maintaining a desired geometry orgenerating slight changes in journal shape desirable for providing thejournal profiles mentioned above pursuant specifications.

Typical crankshafts have two or more main bearing journals, located onthe axis of rotation of the crankshaft, and one or more eccentricconnecting rod journals which move in an orbital path relative to thecrankshaft axis of rotation. Typically a tool is brought into contactwith the bearing journal and is oscillated during machining in thedirection of the cylindrical axis of the journal during relativerotation between the tool, the abrasive agent and the journal surface toenhance material removal and eliminate machining debris and abrasiveparticles. Microfinishing tooling for internal combustion crankshaftsmust operate within the confines of the axial length of the journalbearing surface being machined since crankshaft structures such as thethrows, webs, flanges, and gears present between the bearing surfacesinterfere at the axial ends of the journals. Therefore, typicalcrankshaft microfinishing machines use a pair of arms extendingperpendicular to the crankshaft axis of rotation which clamp onto thebearing journals during machining. High production rate machines providesimultaneous microfinishing of multiples or all the the crankshaftbearing journal surfaces of a crankshaft.

Manufacturers of internal combustion engines and component manufacturersseek to minimize the capital expenditure of machining equipment. This isa factor in terms of the number of machines and tooling configurationswhich must be operated and maintained. Flexibility of machining systemsfor microfinishing is a significant advantage, provided that machiningperformance and part production rate goals can be simultaneously met. Atpresent, microfinishing tooling of the type described above typicallymust be designed and produced specifically for workpieces with journalshaving a given axial length and diameter, and desired surface shapeprofile. Present crankshaft microfinishing tooling has a width justslightly less than the width of the crankshaft journal, with sufficientclearance to provide desired oscillation of the tool during themicrofinishing process. Micromachining workpieces with differentdimensional specifications typically requires tooling changeover withthe attendant operational downtime and manpower commitments. It is afurther object of the present invention to provide enhanced flexibilityfor microfinishing tooling and machines.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus and methodsspecifically suited for crankshaft microfinishing are describedproviding numerous benefits over current techniques and devices. Twoprincipal features are described, one feature enables providingstandardized machines and tooling for a variety of crankshaftconfigurations. Another area of enhancements according to the inventionis related to producing desired journal bearing surface shape. Bothfeatures of the invention are realized utilizing microfinishing toolingwith shoes having a width significantly less than the axial length ofthe journal surface to be machined. The narrow tooling width or “thinshoe” design permits journals over a range of axial length to bemachined using common tooling. In one implementation of the presentinvention, a shoe width is less than 50% (and preferably less than 40%)of the journal bearing axial length, while greater than about 20% of thelength. Additional benefits are provided through precise control overone or more of various machining parameters during microfinishingincluding, applied shoe clamping force, tool oscillation, and toolstroking which can be implemented to generate the desired journalprofile shapes. These parameters take advantage of the tailoredmachining capabilities using the “thin shoe” configuration since theypermit regions of the journal surface to be machined with a differenteffect than other regions. Furthermore, with sufficient compliance inthe tooling backing, some flexibility of journal diameter can also beaccommodated with individual tools.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a representative crankshaft workpieceloaded into a microfinishing machine in accordance with the presentinvention showing the driving headstock and tailstock, and illustratingan oscillation mechanism, but shown without the microfinishing clampingarms.

FIG. 2 is a pictorial view of a representative crankshaft workpiece inaccordance with the present invention shown with the microfinishingclamping arms.

FIG. 3 is a cross-sectional view taken along line 3-3 from FIG. 2particularly showing the microfinishing tooling and crankshaft journal.

FIG. 4 is a partial enlarged and cutaway section of a representativecrankshaft showing a main bearing journal or a rod bearing journaldivided into three sub component regions of the axial length of thebearing journal surface.

FIGS. 5(A), (B) and (C) are charts illustrating representative schedulesfor generating desired journal bearing surface profiles by varying shoeclamping pressure during a microfinishing process.

FIGS. 6(A), (B) and (C) are charts illustrating representative schedulesfor generating desired journal bearing surface profiles by varying shoeoscillation frequency during a microfinishing process.

FIGS. 7(A), (B) and (C) are charts illustrating representative schedulesfor generating desired journal bearing surface profiles by varying toolstroking schedules during a microfinishing process.

DESCRIPTION OF THE INVENTION

FIGS. 1, 2 and 3 illustrate a microfinishing machine 10 in accordancewith the present invention and which is capable of being operated topractice the methods in accordance with the present invention. As shownby the figures, a representative workpiece shown as internal combustionengine crankshaft 12 is supported at opposing ends by machine headstock14 and tailstock 15 which together cause crankshaft 12 to be rotatedabout its longitudinal center axis 18. Crankshaft 12 forms a number ofcylindrical journal bearing surfaces to be microfinished, including mainbearing journals 20 (four shown in FIG. 1) which are concentric withaxis 18, and rod bearing journals 22 (six shown in FIG. 1) which move inrotational and orbital paths upon rotation of crankshaft 12. Sincecrankshaft 12 is rotated about its longitudinal axis 18 which is coaxialwith main journals 20, their centers remain theoretically stationaryduring rotation of the crankshaft. Crankshaft 12 includes a number ofstructures such as throws or webs 24 which provide for the eccentricpositioning of the rod bearing journals 22 and provide counterweightsfor balancing the crankshaft during operation in an engine. Additionalstructures including pinion shaft 26 and central drive sprocket 28 ofthe representative crankshaft 12 are shown. The presence of theseadditional structures limits the axial length within whichmicrofinishing tools must operate. In other words, these structurespresent obstacles preventing microfinishing tooling from stroking beyondthe axial ends of the journal surfaces being microfinished. It is notedthat the configurations of crankshaft 12 illustrated in FIGS. 1 and 2differ slightly; namely, crankshaft 12 in FIG. 2 features five mainbearings 20 and four rod bearings 22, and does not include drivesprocket 28. However, these are examples of typical crankshafts subjectto machining operations in accordance with the present invention andthese differing features do not limit the implementation of the presentinvention.

In order to provide oscillation during a microfinishing process, whichis described in more detail in the following description, ball screwshuttle mechanism 30 is operated to cause reciprocation of headstock 14during microfinishing operations. Tailstock 16 is provided with acompliant element such as an air spring (not shown) which allowscrankshaft 12 to oscillate in a reciprocating manner along its centralaxis 18. Oscillation is characterized as small displacements operate ata higher frequency than another type of longitudinal motion described inmore detail below termed stroking. Microfinishing machine 10 is operatedunder computer numerical control by controller 15 and is used withmaterial handling equipment, enabling crankshaft 12 to be loaded into aposition between headstock 14 and tailstock 16 which are operated tosupport the crankshaft for rotation. A rotational drive system (notshown) is provided to drive rotation of crankshaft 12 duringmicrofinishing operations.

Referring in particular to FIG. 3, microfinishing tooling 32 includesupper shoe 34 and lower shoe 36. Shoes 34 and 36 are supportedrespectively by upper and lower arms 26 and 28. With specific referenceto FIG. 3, arms 38 and 40 are shown supporting shoes 34 and 36 mountedto the arms. Each of the shoes 34 and 36 forms a semi-cylindricalmachining surface 42. A number of tool inserts 44 are mounted to theshoes 34 and 36 and can be formed of hard materials such as ceramics, orcompliant materials such as urethane based compounds, as a few examples.Inserts 44 are machined or formed to generate the semi-cylindricalmachining surfaces 42. Microfinishing film 46 is pressed against therespective journal bearing surface by the inserts 44 and has a surfacecoated with an abrasive material. In another implementation, machiningsurfaces 42 can be formed by an abrasive material which directly acts onthe workpiece surface without using and intermediate abrasive film 46.Rotation of crankshaft 12 causes relative motion and machining actionbetween microfinishing film 34 and the journal surfaces 20 and 22. Upperand lower arms 38 and 40 exert a clamping force F, forcing theassociated shoes 34 and 36 against film 46 and the journal surface beingmachined. As previously mentioned, rod bearing journals 22 undergoorbital motion and accordingly the associated upper and lower arms 26and 28 engaging the rod bearing journals follow this orbital path duringmachining.

A representative microfinishing machine 10 has multiples of upper andlower arms 38 and 40, and respective tooling for engagement with each ofthe rod and main bearing journals 20 and 22. Accordingly, during amachining operation, rotation of crankshaft 12 provides machining actionfor each of the bearing journals. When using microfinishing film 46, thefilm is indexed between machining cycles so that a fresh abrasivesurface patch acts on the journals during a machining sequence. Upperand lower arms 38 and 40 open following a machining operation to permitunloading of crankshaft 12. Once a new part is positioned between themachine headstock 14 and tailstock 16, arms 38 and 40 are moved to clampagainst the journal surfaces under computer numerical control bycontroller 15. Microfinishing machine 10 further includes strokinglinear actuator 48 which causes each of the clamping arms 38 and 40stroke across the axial width of the respective bearing surfaces 20 and22 in a precise manner. Preferably such stroking causes all of theclamping arms 38 and 42 acting on the crankshaft to move together. Whenmachining crankshafts 12 having significant axial length differencesbetween their main bearing journals 20 and rod bearing journals 22,separate sequentially operated microfinishing machines 10 may be used,one for the bearing journals having a particular axial length and strokedisplacement, and another for the bearing journals having a differingaxial length and stroke displacement. An example of such multipleoperations is used for crankshafts having so-called split pin rodbearing journals with a single rod journal 22 supporting two connectingrods. Such a sequential process is referred to in the industry as“stitching”.

As best shown in FIG. 2, upper and lower shoes 34 and 36 define a widthw. Journals 20 and 22 define an axial width (or length) W, which asmentioned previously may differ between the journals 20 and 22. Asshown, journals 20 and 22 typically have accurately machined cylindricalsurfaces with the axial ends forming relief or oil grooves 50. Due tointerference with the crankshaft throws 24 or other structures, it ispossible with these types of workpieces to move shoes 34 and 36 axiallyonly within the confines of the length of the respective bearingjournals or until interference with the throws 24 or other structureswould occur.

In addition to microfinishing machine 10 having the capabilities ofcontrolling the clamping pressure F exerted by upper and lower arms 38and 40, control over the axial position of the arms and tools along theaxial length of the journals is also provided by stroking linearactuator 48, again under numerical control by controller 15. Axialmotion of the tooling during machining can be provided in twocategories; termed oscillation and stroking. Oscillation of the toolsmentioned previously is characterized as a high frequency (e.g. 5-300Hz) and small magnitude relative motion (e.g. 1-2 mm) provided toenhance the cleaning effect for the abrasive agent during microfinishingmachining. Typically, liquid machining fluids are used to carry awayabrasive particles and metal waste material removed duringmicrofinishing. This oscillation movement is provided by ball screwshuttle 30. Arms 26 and 28 are also controlled by controller 15 toprovide a desired stroking motion under control of stroking linearactuator 48, characterized as causing the shoes 34 and 36 to movelinearly across the entire or a substantial portion of the axial lengthof the journal being microfinished.

In accordance with a feature of the present invention, tooling width wis chosen to be less than 50% and greater than about 20% of the axiallength W of journals for a class of crankshafts 12 to be machined (or0.2 W≤w≤0.5 W). Preferred embodiments have an upper range of width w ofequal to or less than about 40% of the axial length W (i.e. 0.2 W≤w≤0.4W). By choosing w to be less than one-half the journal length W for ajournal having the shortest axial length of a class of crankshafts to bemachined, a range of greater length bearing journal crankshafts can bemachined using the same tooling 32, while still satisfying the aboveexpressed dimensional range. In accordance with this invention, with thenarrow “thin shoe” width w defined herein, the shoes 34 and 36 arestroked across the axial length of the journals to provide a machiningeffect along their entire length. Moreover, by modifying the dynamicposition of the tools and/or the clamping force F acting on the tools ina prescribed schedule, desired machining effects can be provided. Shoes34 and 36 are positioned and moved dynamically throughout a machiningcycle under numerical control by controller 15. In order to implementthe custom machining effects described herein it is preferred that thetool can be stroked to the axial ends of the journal surface beingmachined while the axial center of the journal is not machined. Thisleads to the “less than 50%” parameter mentioned above. When machiningsplit pin rod journals 22, the tooling width w is likely to approach thelower end of the width range mentioned previously.

In a typical microfinishing process using machine 10 and the processesdescribed herein, a material removal of around 6 μ can be achieved forcast iron and forged steel crankshafts. A machining process willtypically involve several strokes of the tooling across the axial lengthof the journal. In one example, six passes or cycles of stroking of thetooling may be provided, with each pass occurring during a period ofabout 1 second (i.e. stroking frequency of 1 Hz.). During such stroking,oscillation may occurs during the entire machining cycle.

The tooling and machining system according to the present invention iscapable of providing desired journal profile shape in a number of wayswhich may be used independently or in combination to produce the desiredresults. Three approaches are described which involve varying orcontrolling a machining parameter or multiple parameters as a functionof the axial positioning of the tooling along the journal surface,including; 1) clamping pressure, 2) oscillation, and 3) dwell time (orstroking schedule).

FIG. 4 identifies three positions or areas of the tooling along theaxial length of a representative bearing journal (which can be a mainbearing journal 20 or a rod bearing journal 22). In a simplifiedconfiguration, the journal axial length can be thought of as composed ofthe three illustrated axial length sub-components; 52, 54, and 56 (withsubcomponents 52 and 56 at the axial ends, and 54 at the center). FIG. 4shows the tooling in the three region positions.

Now with reference to FIGS. 5(A-C), 6(A-C), and 7(A-C), some of thecontrolled machining parameters mentioned above are described in moredetail. For each of these graphs in FIG. 5(A-C), 6(A-C), and 7(A-C), aline is shown which exaggerates the journal profile surface forillustration purposes. FIGS. 5(A), 6(A) and 7(A) illustrate a so-called“barrel” or convex journal profile in which the middle component 54(axial center) has a slightly larger diameter than end components 52 and56. FIGS. 5(B), 6(B) and 7(B) illustrate a so-called “hourglass” orconcave profile form in which end components 52 and 56 have a slightlylarger diameter than center component 54. FIGS. 5(C), 6(C) and 7(C)illustrate a so-called “double barrel” profile form which is equivalentto two of the convex forms of FIGS. 5(A), 6(A) and 7(A) in a co-lineararrangement, particularly used for so-called split pin journalsdescribed previously.

In FIGS. 5(A-C) clamping force F exerted on the tooling by clamping arms38 and 40 is varied as a function of the position of the tooling 32along the axial length of the bearing journal surface. In these Figures,symbols “+” or “0” are used to show a relatively higher and a relativelylower clamping pressure, respectively. To generate the barrelconfiguration of FIG. 5(A), clamping pressure F is at the higher “+”level when the tooling is in the position of the axial end subcomponents52 and 56, and reduced while the tooling is at the position of centercomponent 54. Thus clamping pressure F is less at the center section 40than at the axial ends 38 and 42. With less clamping force F “0” exertedon the tooling while positioned at the center section 54 of the journal,a less aggressive machining action occurs there and accordingly lessmaterial is removed. By providing the increased “+”clamping force F atthe axial ends 52 and 56 with the reduction “0” at the center 54, adesired barrel shape profile can be generated when starting with acylindrical journal surface. Generating the concave surface profileconfiguration of FIG. 5(B) and the double barrel configuration of 5(C)is achieved using the indicated clamping force F schedules shown inthese Figures.

In FIGS. 6(A-C) oscillation frequency Hz acting on the tooling 32provided by ball screw shuttle 30 is varied as a function of theposition of the tooling 32 along the axial length of the bearing journalsurface. In these Figures, symbols “+” or “0” are used to show arelatively higher and a relatively lower oscillation frequency Hz,respectively. For example the “0” level could be 0 Hz (no oscillation)or some small value e.g. 5 Hz, and the “+” level could be at a higherlevel e.g. 200 Hz. To generate the barrel configuration of FIG. 6(A),oscillation frequency Hz is at the higher “+” level while the tooling ispositioned at the axial end subcomponents 52 and 56, and reduced whilethe tooling is at the position of center component 54. The machiningaction is increased as oscillation frequency Hz increases. Thusoscillation frequency Hz is less at the center section 54 than at theaxial ends 52 and 56. With less “0” oscillation frequency Hz exerted onthe tooling 32 while positioned at the center section 54 of the journal,a less aggressive machining action occurs and accordingly less materialis removed in that region. Conversely, by providing the increased“+”oscillation frequency Hz at the axial ends 52 and 56 with thereduction at the center 54, a desired barrel shape profile can begenerated when starting with a cylindrical journal surface. In otherwords, the diameter D of the journal at the axial center region 54 iscontrolled by controller 15 to be slightly greater than the diameters Dmeasured at the axial ends 52 and 56 of the journal. Generating theconcave surface profile configuration of FIG. 6(B) and the double barrelconfiguration of 6(C) is achieved using the indicated oscillationfrequency Hz schedules shown in the Figures varied between the relativevalues “+” and “0”.

In FIGS. 7(A-C) the stroking schedule acting on the tooling 32 providedby stroking linear actuator 48 is a controlled and varied by controller15 as a function of the position of the tooling 32 along the axiallength of the bearing journal surface. In these Figures, symbols “+” or“0” are used to show a relatively higher and a relatively lower dwelltime or inversely stroking axial velocity at the mentioned bearingareas, respectively. Thus the tooling may be stroked along the journalsurface and cause to dwell or park at the end positions 52 and 56 for aspecified time period before the direction is reversed to traverseacross the journal surface. This again results in greater materialremoval rate at the axial ends to provide the desired profile shapementioned previously. For example the “0” level could be a dwell time of1.0 second and the “+” level could be at 0.5 seconds to generate thebarrel configuration of FIG. 6(A). The machining action is increased asdwell time increases. Thus dwell time is less at the center section 54than at the axial ends 52 and 56. With less dwell time “0” exerted onthe tooling 32 while positioned at the center section 54 of the journal,a less integrated machining action occurs and accordingly less materialis removed. By providing the increased “+” dwell time at the axial ends52 and 56 with the reduction at the center 54, a desired barrel shapeprofile can be generated when starting with a cylindrical journalsurface. In other words, the diameter D of the journal at the axialcenter region 54 is controlled by controller 15 to be slightly greaterthan the diameters D measured at the axial ends 52 and 56 of thejournal. Generating the concave surface profile configuration of FIG.7(B) and the double barrel configuration of 7(C) is achieved using theindicated dwell time schedules shown in the Figures varied between therelative values “+” and “0”.

The above desired journal surface profiles are described as being one ofbarrel, hourglass, or double barrel configurations. It should be notedthat an idealized cylindrical i.e. constant diameter surface may also bea desired configuration.

A preferred feature of the tooling in accordance with this invention isits narrow width w (mentioned previously as a less than 0.5 W) whichallows the variation in machining effect to be provided.

The capabilities of the present invention can be provided in variousmanners. For example, a desired bearing journal surface profilespecified by a customer can be provided by accurately gauging incomingparts to determine their machined surface characteristics. For example,after a grinding operation, a set of crankshafts 12 may have one of thesurface profile configurations described previously, or can exhibitjournals with nearly idealized constant diameter cylindrical profile. Byutilizing the custom variation capabilities of the present invention, adifferent surface profile configuration can be impressed in theworkpiece journal surface even where the workpieces are provided beforemicrofinishing with a different configuration. Also, the surface profileconfiguration provided in incoming parts can be precisely preservedusing these controllable machining parameters.

The above approaches are described in relation to discrete journal axiallength sub-component regions 52, 54, and 56. It should be noted that inimplementing the present invention, the tooling position across thejournal surface can be divided into any number of more narrowly definedaxial length sub-components (to infinitesimally small subregions).Discussion of the three sub-component regions above was chosen as oneway of describing the principles of the present invention. Where suchfiner subsections of axial length are specified a gradual change betweenthe parameters “+” and “0” would be provided.

While the above description constitutes the preferred embodiment of thepresent invention, it will be appreciated that the invention issusceptible to modification, variation and change without departing fromthe proper scope and fair meaning of the accompanying claims.

1. A microfinishing process for processing journal bearing surfaces of acrankshaft, the crankshaft of a type having bearing journals includingat least one main bearing journal and at least one pin bearing journal,one or more of the bearing journals bound on axial ends by crankshaftwebs or other radial obstructions, each of the bearing journals definingan axial length, comprising the steps of; providing tooling in the formof at least a pair of microfinishing shoes adapted to be clamped andunclamped from the bearing journal, providing the tooling having anaxial width of less than 50% of the bearing journal axial length andgreater than 20% of the bearing journal axial length, rotating thecrankshaft relative to the tooling to provide a machining effect on thejournal bearing surface, and causing the tooling to stroke along theaxial length of the bearing journal between the axial ends when rotatingthe crankshaft relative to the tooling providing the machining effect.2. A microfinishing process in accordance with claim 1 furthercomprising providing the bearing journals includes providing the bearingjournals having a range of the axial lengths.
 3. A microfinishingprocess in accordance with claim 1 further comprising varying amachining parameter while providing the machining effect including oneor more of; clamping pressure of the tooling, oscillation of thetooling, and dwell time or stroking velocity of the tooling.
 4. Amicrofinishing process in accordance with claim 1 further comprisingvarying a machining parameter while providing the machining effect as afunction of the axial position of the tooling along the axial length ofthe journal bearing.
 5. A microfinishing process in accordance withclaim 1 further comprising varying a machining parameter by adjustingthe clamping pressure exerted on the tooling as a function of theposition of the tooling along the axial length of the journal surface.6. A microfinishing process in accordance with claim 1 furthercomprising varying a machining parameter by adjusting the oscillationfrequency of the tooling as a function of the position of the toolingalong the axial length of the journal surface.
 7. A microfinishingprocess in accordance with claim 1 further comprising varying amachining parameter by adjusting the oscillation displacement of thetooling as a function of the position of the tooling along the axiallength of the journal surface.
 8. A microfinishing process in accordancewith claim 1 further comprising varying a machining parameter byadjusting the stroking schedule of the tooling as a function of theposition of the tooling along the axial length of the journal surface.9. A microfinishing process in accordance with claim 1 furthercomprising rotating the crankshaft relative to the tooling during themicrofinishing process.
 10. A microfinishing process in accordance withclaim 1 further comprising wherein the tooling pressing an abrasivecoated film against the bearing journal when the tooling is clampedagainst the bearing journal.
 11. A microfinishing process in accordancewith claim 1 further comprising providing the tooling in the form of apair of shoes supported by clamping arms.
 12. A microfinishing processin accordance with claim 1 further comprising the step of causing thetooling to stroke along the axial length of the bearing journalincluding the tooling crossing the axial center of the journal bearingsurface and at positions of the tooling at the axial ends of the bearingjournal, the tooling is not acting on the bearing journal surface at theaxial center.
 13. A microfinishing process in accordance with claim 1further comprising the step of providing a desired profile shape for thebearing journal surface including one of a constant diameter form, abarrel shape form, an hourglass shape form, and a double barrel shapeform by varying a machining parameter while providing the machiningeffect as a function of the axial position of the tooling along theaxial length of the journal bearing.
 14. A microfinishing apparatus forprocessing journal bearing surfaces of a crankshaft, the crankshaft of atype having bearing journals including at least one main bearing journaland at least one pin bearing journal, one or more of the bearingjournals bound on axial ends by crankshaft webs or other radialprojections, each of the bearing journals defining an axial length,comprising; tooling in the form of at least a pair of microfinishingshoes adapted to be clamped and unclamped from the bearing journals, thetooling having an axial width of less than 50% of the bearing journalaxial length and greater than 20% of the bearing journal axial length, adrive for rotating the crankshaft relative to the tooling to provide amachining effect on the journal bearing surface, clamping arms whichposition the tooling to engage the bearing journal surface and press thetooling against the bearing journal surface, a shuttle for causing thetooling to oscillate along the axial length of the bearing journal, andan arm stroking actuator for causing the tooling to stroke along theaxial length of the bearing journal along the axial length of thejournal when the drive is rotating the crankshaft relative to thetooling providing the machining effect.
 15. A microfinishing machine inaccordance with claim 14 further comprising the bearing journalsincludes providing the bearing journals having a range of the axiallengths.
 16. A microfinishing machine in accordance with claim 14further comprising a controller for varying a machining parameter whileproviding the machining effect including one or more of; clampingpressure of the tooling, oscillation of the tooling, and dwell time ofthe tooling.
 17. A microfinishing machine in accordance with claim 14further comprising a controller for varying a machining parameter whileproviding the machining effect by varying as a function of the axialposition of the tooling along the axial length of the journal bearing.18. A microfinishing machine in accordance with claim 14 furthercomprising a controller varying a machining parameter by adjusting theclamping pressure exerted on the tooling as a function of the positionof the tooling along the axial length of the journal surface.
 19. Amicrofinishing machine in accordance with claim 14 further comprising acontroller for varying a machining parameter by adjusting theoscillation frequency of the tooling as a function of the position ofthe tooling along the axial length of the journal surface.
 20. Amicrofinishing machine in accordance with claim 14 further comprising acontroller for varying a machining parameter by adjusting theoscillation displacement of the tooling as a function of the position ofthe tooling along the axial length of the journal surface.
 21. Amicrofinishing machine in accordance with claim 14 further comprising acontroller for varying a machining parameter by adjusting the strokingschedule of the tooling as a function of the position of the toolingalong the axial length of the journal surface.
 22. A microfinishingmachine in accordance with claim 14 further comprising the driverotating the crankshaft relative to the tooling during themicrofinishing process.
 23. A microfinishing machine in accordance withclaim 14 further comprising wherein the tooling pressing an abrasivecoated film against the bearing journal when the tooling is clampedagainst the bearing journal.
 24. A microfinishing machine in accordancewith claim 14 further comprising the tooling in the form of a pair ofshoes supported by clamping arms.
 25. A microfinishing machine inaccordance with claim 14 further comprising the stroking actuatorconfigured for causing the tooling to stroke along the axial length ofthe bearing journal including the tooling crossing the axial center ofthe journal bearing surface and at positions of the tooling at the axialends of the bearing journal, the tooling is not acting on the bearingjournal surface at the axial center.
 26. A microfinishing machine inaccordance with claim 14 further comprising a controller to configuredfor providing a desired profile shape for the bearing journal surfaceincluding one of a constant diameter form, a barrel shape form, anhourglass shape form, and a double barrel shape form by varying amachining parameter while providing the machining effect as a functionof the axial position of the tooling along the axial length of thejournal bearing.